Cross-drilled brakes a fraud?

[aNoodle]

Do you agree, cross-drilled brakes are "largely a cosmetic touch," "not generally a good idea?" In discussing the new Corvette, Motor Trend says.....

"We asked why the Z51 brakes are cross-drilled, and were told that there's perhaps a slight improvement in cooling of wet brakes, and maybe a bit more initial bite, but the engineers admitted it was largely a cosmetic touch. The aftermarket guys are all doing it, so customers think it's a good thing. Drilling an existing rotor reduces the surface area swept by the pads and removes mass that would otherwise serve as a heat sink in preventing brake fade, so it's not generally a good idea. But the new Z51 brake rotor diameters are larger by 0.6 inch in front and an inch in the rear, and they feature smaller internal cooling vent passages so that their mass is actually increased by 2.2 pounds each in front, 1.8 pound each in back, providing plenty of fade resistance, holes or no holes. And these rotors aren't shaped like a simple hat, with the swept area being the brim, and the place where it bolts to the axle the stovepipe. Rather, the stovepipe and brim are connected by a unique J-section--picture a gutter around the stovepipe. This reduces hot spots and prevents the thermal distortion that results in rotor warpage."

http://motortrend.com/features/performance/112_0408_corvette_tech/index1.html

 

[wood_e]

I agree they're mostly for looks. People think it's racy. The fact is cross drilled rotors are prone to cracks. They're generally a bad idea, and when the time comes for a new rotos you cannot turn cross drilled rotors. Slotted rotors are a much better alternative and actually have more benefit.

 

[epj3]

Slotted are better from what i've heard?

 

[knightpitt]

I run ATE Powerslot and have no regrets. I also would have no fear about getting, say, Brembo crossdrilled rotors. Off-brand crossdrilled? Forget it. Chevy is certainly not the only manufacturer that stocks OEM crossdrilled. Porsche has offered them for a while and I am certain that there are plenty of others as well.

Not being a materials science expert, I can't speak specifically about the heat dissipation qualities of the different types of rotors, but reducing the cooling channel size in order to have cross-drills seems couneter productive to me. They decreased the roational mass and the amount of mass that could be used as a heatsink by cross-drilling the rotors but the drills also increase the cooling efficiency. Then they reduced the size of the cooling channels (presumably by thickening the braking surface as well - 2.2 lbs is a fairly large amount of weight for a 0.6" diameter increase), effectively reducing the cooling capabilities and increasing the roatational mass. And, they also slightly increased the diameter of the rotor as well. Overall net effect: maybe a bit better braking power at the expense of more rotational mass. The bottom line: it's effectively for cosmetic effects.

In a racing application, you'll find that cross-drilled rotors will be significantly lighter for their braking power and fade resistance than comperable solid rotors. The cross-drills provide higher cooling efficiency, thus requiring less mass for the purpose of fade resistance. In fact, I wonder why Chevy ended up with heavier rotors. It seems to me that they either did not want to risk the higher failure rate of "real" crossdrilled rotors or did not want to put in the engineering time to refine the technology appropriately. However, neither may end up being true.

On a related note, the ATE Powerslot rotors that I installed on my Jetta made a world of difference in "spirited driving" for me. Whereas plain rotors would have terrible and unsafe fade when driving in a spirited fashion, my ATE's have performed admirably with no sign whatsoever of fade in even more adverse conditions than I subjected the solid rotors to.

So, to kinda answer your question, I'd buy the ATE's again, and will for my E36 the first time that I need new pads.

 

[BMW-M-Freak]

OK, guys. I went to a set of cross drilled rotors on my E30 318 about 4 months ago. Sure they look good, but i think they actually do have a few more performance perks than a standard rotor. I've always understood the holes as a way for the gasses and dust to vent from between the pads and the rotor (same is true for slotted) under spirited driving. AS for as not having as much of a contact patch, this is true. I don't think under normal driving the cross drilled ones that i have on mine will bite as hard in a pinch. But after about 2 or 3 hard stops...... those cross drilled ones will pour on some serious stopping power. I def. noticed a reduction in brake fade under hard driving.

Side note: If you're looking for a performance rotor for the street, go slotted. It doens't have as much of a tendency to crack like cross drilled, but it'll still have you eating the steering wheel when you wanna stop.

 

[epj3]

Cross drilled crack. The thing is - on my car, you wouldn't get any visual gain becuase of the wheel design.

http://www.bmwchannel.com/epj3/PICT0002.jpg

 

[MrElussive]

This debate comes up a lot about cross-drilled rotors. The fact is, they generally reduce mass and offer some cooling through those holes. Cross-drilled brakes are better for a "performance street" setup, but if you want better heat resistance, you gotta go with slotted rotors. Cross-drilled rotors are not only for "show".
For example, both my parents' 04 S500 4Matic's have cross-drilled rotors up front. Both cars do not have the Sport Package and we can generally agree that the S500 really isn't made for sporting intentions (or at least the level of luxury is way beyond the level of performance) but both cars' front rotors have this cross-drilled setup.
It definitely does look more sporty with a cross-drilled setup and it's simply ironic that slotted rotors are better version. Basically, if you never take your car to the track and you want performance braking and you like the look of the holes, then cross-drilled rotors are for you. If you take your car on the track or if you don't like the look of the holes, then slotted rotors are your best bet.

 

[Ghost]

I think slotted are best for cars with small brake rotors because they have more surface area, weight for heat distribution and the slots allow the gases to escape in the process. If you can go big then all around I think X-drills are best, primarily for the larger applications because the cooling can be done over a comparable surface area with a large diameter rotor. Plus the holes allow the gases (and water) to be dispersed more rapidly from the surface. Just my $.02

 

[MrElussive]

Yeah I agree with you Ghost. A lot of brake experts say that the holes actually do not really help with cooling and venting much at all, but I'm inclined NOT to believe them.

 

[Section_8]

Good posts, returning hot topic!

Slotted and Drilled.. Well unless you are really hitting the track alot or have a high HP car (both reasons to want to reduce heat quickly), they are cosmetic pure and simple.. Yes, they do assist with the cooling of the brakes and reduce fade - for the track or on real sports cars (IE: BBK's come stock on Porsche's..). Only slightly on a daily driver car, you got to be doing some serious spirited driving to ever need a drilled/slotted on a daily (unless you meet that sports car level). However having drilled/slotted can also lead to brake seizure more often, and they are more prone to cracking, and depending on quality/manufacturer will not last as long as normal OEM rotors, much less good aftermarket (brembo) 'normal' rotors. This from my friend who does my brakes that is a mechanic for a BMW race team occasionally seen on speedworld (Team slips me, the yellow/baby blue guys if you're watching on the weekends. He works on the car that is sporting the Umnitza DDE angel eyes).

Mr. E - The reason you see them on MB's is again for looks, it's a MB what else is it good for? (muhaha that should get the MB trolls hopping!) Seriously though, MB's are also heavy cars (even more than BMW's) so more weight = more friction = more heat, so I can see why some MB's might have a 'real' need for slotted or drilled. I'm sure MB's slotted are also quality parts (at least you'd hope!).

If you want them (and why not, they do look hot, my bud talked me out of them though) make sure you get MANUFACTURED drilled or slotted, and not some fool aftermarket's attempt by drilling normal rotors (this happens and is sold more than you would think).

 

[MrElussive]

Section_8, that was my point. For a vehicle like the S500, I really do not understand why cross-drilled rotors would help out its looks at all. The rims cover up the rotors pretty well and the S500 is just not a car for sporting intentions really, which is why I am concluding that the cross-drilled rotors must help somewhat in brake cooling and that looks have nothing to do with it (the S-Class being a luxury sedan). More specifically, it is only the front rotors that are cross-drilled, the rears are just normal rotors. I cannot speak for other MB's, I can just speak for the S500 as my parents have two of them....one of which is in service because my mom's car seems to not want to play any music when it doesn't feel like it!!!!!!!!!!! hahahahahahhaa !!!!!!!!!!!!!!!!!

 

[wood_e]

Way to dig up old threads Emile

 

[tool fan]

I always thought that the cross drilled rotors were more for the weight reduction of the rotors. Ricers swear that their cars gain a .5hp with reduced weight cross drilled rotors. I think that largly they are over priced and exemely over rated. Then again I don't drive a Lambo or Porche or Ferrari or Mseries Bimmer so I do not have an excuse to go by such high priced performance upgrades. If those of you who do have these cars, then have at it, just don't be overly confident that your brakes WON'T fade out during your spirited driving because then the Ambulance driver will be doing some spirited driving to get your hiney to the hospital after you put your car into a tree. One question you guys should be asking yourselves is, who normally does the most radical driving....COPS right? Why don't they sport cross drilled rotors on the the pursuit vehicles?

Sorry I am having a BAD Day!!!!

 

[MrElussive]

Way to dig up old threads Emile

yo but yesterday this thread was new for me. When I read this post, I realized I was the only one who posted anything recent, but I was just on the main page of General Car Chat...didn't even realize Section_8's response was from a million years ago until just now. My bad, I wasn't in the right state of mind.

 

[///M SPEED]

yo but yesterday this thread was new for me. When I read this post, I realized I was the only one who posted anything recent, but I was just on the main page of General Car Chat...didn't even realize Section_8's response was from a million years ago until just now. My bad, I wasn't in the right state of mind.

You did good Emile. It is nice to see you do a search to see if there is an open topic on the subject matter instead of creating another thread, which is OK too. Doing a search is a good way to find a lot of info (new and old) on the topic at hand or questions one may want/need answered. Old threads my have input from members that are no longer here, but contain information or experiences they have encountered......

 

[MrElussive]

Yeah, the weird thing is, I wasn't even looking for this thread, and I wasn't even searching anything. I was just perusing BMWBoard and I stumbled upon it thinking someone resurrected it by making a post and that I was just adding another comment. I'm just all confused how I found this last night, lol.

 

[///M SPEED]

This thread had to be buried pretty deep. If you were drinking you could have accidentally clicked on one of the numbered pages at the bottom of the forum topic page and from there started browsing like it was on page one. That is my bet.....

 

[epj3]

No, the reason it came up is becuase someone voted. if you vote on an old thread, it brings the thread to the top.

 

[Big Daddy]

Darn voters they bring a lot of things to the top!

I liked the idea of it coming up again, I was just talking with a friend who was trying to decide, cross drilled, slotted or stock...he went with slotted.

 

[selavia]

My brother has a v6 camry; not a very quick car; quick enough though. He had the stock set-up on his brakes for quite sometime. He got Brembo cross drilled cadium plated rotors ($125 for the four) and his cars braking ability increased drastically. (He did upgrade the pads, calipers and the line was bled/flushed). When he steps on the brakes hard, it slows down noticeably quicker. I was even amazed. I've driven his and other camry many many times and the brakes have always given room to doubt, but I have to admit his cross drilled along with everything else really made a difference. BTW, the calipers were a toyota upgrade and both old and new were two pistons, and he did not upgrade the rear calipers.

Just my thoughts.

Sean